1. Field of the Invention
This invention relates to a sewing machine provided with an automatic threading apparatus for automatically transferring a needle thread extending from a thread supply to thread a plurality of thread guides.
2. Description of the Related Art
In conventional sewing machines, a needle thread extending from a spool is threaded so as to be passed through a plurality of thread guides (a thread tension regulator, a take-up spring, a thread take-up lever and the like) in a predetermined sequence and via a predetermined path, so that the needle thread is led to a sewing needle mounted on a needle bar. The needle thread is then passed through an eye of the needle, whereupon the sewing machine is capable of sewing. The needle thread is manually passed through the thread guides in many sewing machines. However, a sewing machine provided with an automatic threading apparatus has been put into practical use. In use of the threading apparatus, a needle thread drawn from a spool is passed through a predetermined preparatory path. The threading apparatus automatically transfers the needle thread to thread a plurality of thread guides.
For example, JP-B-H02-14866 discloses an automatic threading apparatus includes a thread holding member, an operating lever having a distal end on which the thread holding member is pivotally mounted and a proximal end pivotally mounted on a machine frame, a thread carrying member having a distal end formed with an engagement portion and a proximal end pivotally mounted on a machine frame, and an operation unit. A thread tension regulator is provided at a position confronting an upper side of a sewing arm. When a needle thread is to be set so that sewing is executable, firstly, the needle thread extending from the spool is passed through the thread tension regulator, the thread guide of the take-up lever and the thread holding member in this sequence while a thread guide provided on a distal end of a thread take-up lever, the thread holding member and the engagement portion of the thread transferring member are caused to protrude to the upper side of the sewing arm for preparation.
When the operation unit is operated under the aforesaid condition, the operating lever and the thread transferring member pivot so that the thread holding member holding the needle thread is lowered near to the sewing needle. The needle thread is passed through the eye of the sewing needle by an automatic needle threader having a threading hook. Further, the needle thread is than caught by the engagement portion of the thread transferring member, and the thread transferring member is then lowered so that the needle thread is caught by a take-up spring disposed in the sewing arm. Threading needs to be manually carried out when the needle thread cannot automatically be passed through the thread guides for the reason of failure of the automatic threading apparatus or the like.
However, the above-noted reference discloses nothing about a technique of manually passing the needle thread through the thread guides. More specifically, in such a sewing machine as disclosed by the reference, the take-up spring, the thread take-up lever and thread tension discs are disposed in the interior of the sewing machine. Accordingly, it is difficult to manually pass the needle thread through a plurality of thread guides. It is supposed that manual threading is possible when front-side covers of the take-up spring, the thread take-up lever and thread tension discs cover are opened. However, the sewing machine with such an automatic threading apparatus as described in the above-noted reference is not constructed so as to be manually operated to pass the needle-thread through the thread guides. Accordingly, upon occurrence of failure in the automatic threading apparatus, it is difficult to pass the needle thread through the thread guides. For example, the needle thread cannot be passed through the thread guides easily and reliably until the threading apparatus is recovered from the failure, whereupon there is a possibility that this would cause troubles to sewing.
On the other hand, it is suggested that the front-side covers of the take-up spring, the thread take-up lever and thread tension discs cover be constructed to be normally openable so that manual threading becomes possible. However, the covers need to be opened when the manual threading is to be carried out, and the covers need to be closed after the manual threading has been carried out. Thus, a troublesome work is required. Further, even when the covers are closed, there is no guarantee that the needle thread can be passed through the thread guides readily and reliably. Furthermore, there is a possibility that foreign matter may fall into the interior of the sewing machine during opening of the covers, resulting in failure.